Protective system



p 1933- H. NEUGEBAUER 2,130,896-

PROTECTIVE SYSTEM Filed Aug. 5, 1933 2 Sheets-Sheet 1 A'A'A All A .92 15% 74 M500 A A M600 7; 7m A 500 400 0 0 70 0 600 O A 40 72) A7550 A so'o 74) 750 A 5.50 2 50 0 750 650 O A B C WITNESSES: INVENTOR fiermam/Veayehaez' ATTORNEY Sept- 1933- H. NEUGEBAUER' 2,130,896

PROTECTIVE SYSTEM Filed Aug. 5, 1933 2 Sheets-Sheet 2 Demadu/afedcurren I fieuirercirca/f Modu/af/hg Circuif F i/fer Fi/fer poss'i 550'" F/lfer WITN ESSEVS 1 c. M 77 INVENTOR rmann 'A/eqge houer BYQa a g I ATTORNEY Patented Sept. 20, 1938 2,130,896

UNITED STATES OFFICE 2,130,896 PROTECTIVE SYSTEM Hermann Neugebauer, Berlin-Spandau, Germany, assignor to Westinghouse Electric "8; Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application August '5, 1933, Serial No. 683,893 In Germany August 8, 1932 27 Claims. (Cl.=1'l5-294) My invention relates to protective systems for at all selective lnandof themselves, but become transmission lines. selective only by comparing the current-condi- N merous protective systems-have beenprotions at --oneend of the line-section with the p inv which relaying devices are arranged current-conditions at the other end. If the auxat the end of the protected line-section, the reiliary channel which is-necessary for effecting 5 laying devices being connected ,to one another this-ccmparlson should fail,'faulty operations are through an auxiliary communicating channel unavoidable.

such as a high-frequency path, and being brought Aeeerdihgte the'plesent invention vthe P into such mutual relationship that the opening te vey t m 'wh h' p n p n the p of the circuit-interrupter at each end of the linet e s f t e re y at both ends the1ine-Seeti0n10 section depends not only ,upon the operation of is put'out of operationassoon-as it is ascertained the relay in the neighborhood of the switch, but that'the'transmitter lsfa'iling to transmit. The also upon the operation of the relaying devices putting out of operation is retarded'for a certain at the other end of the line-section. Such sectime, in order that the protective System is not tion-protective systems may be carried out in put-out of operation in such cases in which it is l5 various ways; for instance, in such manner that about to operate. 'An indication of a failure of a signal coming over the communicating chanthe carrier sy y be Obtained from the nel is necessary, if the circuit-interrupter is to f t an op r ion of the earrier'system, be opened, or in such manner that a signal comwhich should take'p y if a f u t has 00- mg over the auxiliary channel is utilized to precurred somewhere in the protected section, is not- 20 vent the opening of the circuit-interrupter. The a p n y operation of he ippin signal may consist in either the transmission or y 0f thepreteetive Y yf instance, the interruption of a signalling current in'the flpp y Over-current yr communication channel. iftheopenin'g of the circuit-interrupter depends The invention, in one of its embodiments, rep n h t that no carrier-current na r- -25 lates to protective systems of the last-mentioned rives' from theremote-end of the section to-block character, in which, if the signal from the re- Said p c-in ease of arfault rrin mote end of the line-section is not transmitted, ut d Ofthe Protected Section, e -t 'an the opening or the circuit-interrupter switch is -misSi0n-of the blocking signal would not alone made possible, or caused to take place in the a e he-opemns f the rr p The :30

shortest possible time. very fact, therefore, that the blocking signal fails According to the invention, thezprotective de- -to flow as circulating current, while-the tripping vices which are provided 'to transmit a highrelay is not actuated, shows the occurrence of a frequency signal from one end of the section to -failure--of thecirculating-current circuit. In this the other, for indicating theoperation ofarelay, a' r t the invention, an auxiliary s5 are continuously controlled or'tested as to-rthelr lay is p r t d-w i the-entire -s n operativeness. To this end, I provide a relaying vprotective system out of Operation after a predevice which operates as a resultof a failure of -determ'medtime-delay for which theau i ary the carrier means. The carrier means comprises relay-isa'djusted. The' subsequent fault-respon- 40 a device which controls the transmission of the sivediscohnection-of the line-section would have 40 signal, a carrier-current transmitter or powerto beefiecte'd, in this case,=by-'asecond protecsource for the signal'to be transmitted'and'in -ti've system, if any; for instance, by a protective case auxiliary lines are provided, these auxiliary system with inverseor definite time grading.

'lines, over which the signal is to be transmitted. 'In the accompanying drawings, Fig. 1. is a dia- If this carrier system fails to operate, it-may 'grammatic view-of-circuits and apparatus illus- =45 happen that the circuit breaker at the other end trating my-invention a's'applied to a line-section 0 e Protected line-Section y be p d'bya of a' transmission-line; Fig. 2 is a similar view of false rela 'ng operation if, for instance, an overa;modifled construction-applied-to-a plurality of current occurs at this other end-and the direction successlvesectlons-of a longer transmission line;

of energy-flow is into the protected-line-section Fig-31s asingle-line diagram of a further modiat said other end. The possibility of this false "fication applied-to a multi-circuit transmission relaying operation is due to the-fact that-the line; aridF-lgA-isadiagrammatic view of circuits individual relaying devices which control the and apparatus illustrative of the equipment at circuit-interrupters in a protective system utilizone of" the sectionalizing-stations in Fig. 3.

" ing an auxiliary communicating channel are not As disclosed in'Flg. 1, my invention is asso- 55 ciated with a three-phase high-voltage transmission system having a line-section 4 which is to be protected. The line-section is provided, at each end, with a circuit-interrupter l which is to be automatically opened by a trip coil 2 as soon as a fault occurs in the section. In the embodiment of my invention shown in Fig. 1, a communicating channel is provided between the two ends of the line-section, in the form of a highfrequency path which extends from earth through a coupling capacitor 3 and one of the line-conductors of the protected line-section 4.

The relaying station at each end of the protected line-section has any suitable power-directional tripping-relay R which is illustrated as being so connected that it responds to the direction of the negative-phase-se quence power-component when there is an unbalanced fault'within the protected line-section. To this end, the power-directional relay R is energized by a negative-phase-sequence current-network I2 and by a negative-phase-sequence voltage-network V2. Each relaying station further includes a transmitter S and a receiving relay E. The transmitter in the station at the left-hand end of the linesection 4 is tuned, for instance, to a frequency of 100,000 cycles, whereas the transmitter at the other end is tuned to 100,500 cycles. The transmitters at both relaying stations normally operate continuously, so that the difiference between the two transmitting frequencies (500 cycles) will normally be continuously available to energize both receiving relays E, as will subsequently be described.

According to the embodiment of my invention shown in Fig. 1, each transmitter S is connected to one of the line-conductors of the section 4, through a normally closed relay-contact 5, and also through atransmitter-coupling transformer 6, a receiver-coupling coil 9, and the previously mentioned couplingcapacitor 3. Each transmitter S is permanently connected, also to a coupling coil l which is inductively related to a coil 8, to which the receiving relay E is connected. The coil 8 is also inductively related to the receiver-coil 9 in series with the coupling capacitor 3. The high-frequency current coming to each relaying station from the distant end of the section thus acts on the coil 8 through the coupling capacitor 3 and the receiver-coupling coil 9. Consequently, the coil 8 has induced therein a voltage of a frequency equal to the difference between the frequencies of the two transmitters E. The voltage induced in the coil 8 operates the receiving relay E only when this voltage has that frequency to which the relay E, or a series-connected filter F, is adjusted, that is, the beat-frequency of both transmitters which are associated with the protective relays of the protected line-section 4.

As soon as the receiver relay E is energized it opens two contacts E1 and E2. When the receiver relay E is deenergized, its contact E1 completes a partial circuit which will result in energizing the trip coil 2 as soon as the power directional relay R has closed its normally open contact R1, provided that the normally closed contact Z1 of a timing relay Z is closed. This timingrelay Z is energized, as soon as the receiver relay E is deenergized, by the receiver-relay contact E2, but the time-relay contact Z1 does not open for a certain time, determined by a dashpot Z2. Thus, if the receiver relay E remains deenergized for this certain predetermined time, without an actuation of the directional tripping-relay R, the time-relay contact Z1 opens and .locks out the carrierand closes both contacts E1 and E2 thereof.

current responsive relaying equipment until proper carrier operation is again restored.

In the illustrated embodiment of my invention, therefore, the protective system is carried out in such manner that the opening of each circuitinterrupter I is normally prevented by a continued transmission of high-frequency current from both ends of the section, which energizes a beat-frequency receiver relay E at each relaying station. In the event of the failure of the beatfrequency, and in the further event of the energization of the directionally responsive trippingrelay R at either relaying station, the corresponding circuit breaker I will be opened.

If a fault occurs in the line-section 4, the power-directional relays R at both ends of the line-section are actuated. The tripping circuit as above described is partly completed through the directional-relay contact R1, the circuit being finally completed as soon as the normally energized receiver relay E ceases to receive its beatfrequency current, so as to close its contact E1.

I The power-directional relay R has also a second normally open contact R2, which closes in response to an unbalanced fault in the protected line-section and energizes an auxiliary relay l which carries the normally closed contact in the circuit of the transmitter-coupling transformer 6. Upon the occurrence of a fault in the protected section, therefore, the transmitter S at each relaying station continues to operate as under normal fault-free operating conditions; but the directional relay R at each end operates, energizing the auxiliary relay l0 and causing the contact 5 to be opened, so that the transmitter-energy is not transmitted to the high-voltage line-section 4 at either end thereof. The influence exerted by each transmitter E on its local receiver-actuating coil 8 is, however, not changed, so that the coil 8 at each station receives energy from only its own carrier-frequency transmitter, although it has no beat-frequency voltage capable of energizing the corresponding receiver-relay E. In this manner, each receiver-relay E is deenergized. Until the timing relay Z picks up its contact Z1, after its predetermined time-delay, the energizing circuit for the trip coil 2 is closed, and hence the circuit breaker 1 opens at each end of the protected line-section.

If the fault is not in the protected line-section 4, but in a neighboring section, for instance in the line-section 20 on the left-hand side of the line-section 4, the receiver-relay E at the righthand end of the protected line-section 4 responds to the inwardly flowing power at this point, and partially closes the tripping circuit at this end of the protected line-section, and it depends only upon the contacts E1 of the receiving relay E at this station to determine whether the-tripping action shall take place or not. At the left hand end of the protected line-section 4, however, the power is flowing outwardly, so that the directional relay R at this end does not respond.

Thus the contact 5 of the auxiliary relay I 0 at this end remains closed, so that the transmitter E at the left-hand end of the protected linesection 4 continues to transmit its high-frequency energy to the right-hand end, where the receiving relay E is consequently supplied with avoltage having the beat frequency corresponding to its tuning. In this manner, the contacts of the receiving relay E remain open at the righthand end of the protected section, so that there is notripping action at that end. At the lefthand receiver relay E and closes its contacts E1, but the tripping circuit at this station is not completed because of the open contact R1 of the unactuated power-directional relay R.

If either one or both of the transmitters E should fail to operate for any reason, a voltage of the beat-frequency cannot result in either one of the receiver relays E, so that these receiver relays in both relaying stations close their contacts E1 and E2. As long as the directional tripping relay R at either end of the line-section does not close its contact R1, the failure of the voltage of beat-frequency is evidently not caused by a line-fault, but by a fault in the carriercurrent system. Consequently, the receiver relays E permanently close their contacts, and the timing relay Z picks up and opens its contact Z1.

Since this timer-relay contact Z1 is series-connected with the trip coil 2, the entire relaying device is thus rendered inoperative, because the selectivity of the entire relaying device depends upon the fact that a mutual cooperation with the relay-device at the other end of the section must be brought about before the opening of the circuit-interrupter I. A faulty opening of a line circuit-interrupter cannot now occur as a result of a failure to receive a signal from the other end of the line-section at a time when the faultenergy at said other end is flowing out of the protected line-section.

In the illustrated embodiment of my invention, as shown in Fig. 1, a single capacitor 3 is schematically shown as the coupling means. In most cases, instead of a simple capacitor 3, a more complicated filter-device is employed, which is tuned to the carrier-current frequencies employed in the protection of the line, and which has a range such that frequencies of a high order of magnitude are permitted to pass. It is preferable to choose high frequencies so as to reduce the dimensions of the transmitting and receiving devices, as well as the filters. For instance,

a carrier-current frequency of 100,000 cycles may be chosen for one end of a protected linesection, and 101,000 cycles for the other end, so that the beat-frequency is extremely small as compared to the carrier-current frequencies employed. It is preferable to choose, for the relaying devices of successive line-sections, frequencies differing slightly from one another, for instance, for two successive line-sections, the frequencies 100,000, 101,000, and 103,000, 104,000, respectively, thus providing a double-frequency (or any different) beat of 2,000 cycles between the 'two transmitter-frequencies in alternate sections, so as not to conflict with the operation of the 1,000-cycle beat-frequency relaying equipment of the intervening sections By connecting the receiving relays to a filter which has a correct range for the beat-frequency employed, a very high selectivity is obtained in regard to the high-frequency currents occurring in the high-voltage transmission lines encountered in the bestquency waves beyond the limits of the several dine-sections, but inwhich this-could be only imperfectly accomplished "by means of blockingcircuits which were built into the high-voltage transmission line and dimensioned for the passage of heavy currents. By the use of the beat frequency it is possible to employ relativelynarrow frequency bands, making'it possible :to' use, for relaying purposes, the intervals which exist between the wave-bands of the telephone,rremote-metering and telegraph communication channels which may be also operatedoverthe -ilo same high-voltage transmission lines.

As shown in Fig. 2, it is possible to reduce the number of different frequencies, that is: to say, to reduce the total range of frequencies, necessary for the protection of several successive line-= sections of a transmission line by using aisingle transmitter in each relaying or sectionalizing-station for two purposes; namely, for the protection of both the right-hand line-section and thezlefthand line-section. In this case, the manner ofugo connection must be alternated, however,: by causing, for instance, the high-frequency carrier-current to prevent the opening of the circuit-interrupter for the line-section o-n the'right-hand side of the relaying station and to open the circuit-egg interrupter for the line-section on theleft -hand side of the station, or vice versa. For various successive sections the number of transmitters, that is, the number of different carrier-currentdrequencies, will not be greater, therefore, thantheugo number of switching or sectionalizing stations.

In Fig. 2 I have shown four successive line-sections of a transmission line, as indicated at'2 I, 22,

23 and 24, separated by sectionalizing relay-stations 25, 26 and 21, respectively. Only one end ofo'gg; each of the sections 2| and 24 is shown in Fig.. 2, the two central sections 22 and .23 beings'shown complete. At each end of each line-section, there is a circuit interrupter as indicated at 28, 29,.30, 3|, 32 and 33, respectively, said circuitbreakers being provided with trip-coils 28' to 33'.

For each end of each line-section there is' a-lso provided a directional relay, as indicated at, 35,

36, 31, 38 and 39, respectively. These directional relays, as in the case of the directional relays R3 in Fig. 1, are each biased to a normal or unactuated position, from which they are moved only in response to power, of fault magnitude, flowing in the direction from the sectionalizing station into the line-section in question. The directional-re--,- lays are shown in their normal or unactuated positions. These directional relays may be 'connected in any known or desired manner of connection, either utilizing the phase-sequence-networks of Fig. 1, so as to respond to a polyphasee phase-sequence quantity, or connected so as to respond to the conditions in individual phases. As the particular method of connecting the directional relays is not essential to an understanding of the modification utilizing a single transmitterno per station, instead of two transmitters as in Fig.

1, I have simplified Fig. 2 by showing only the phase-C directional relays 34 to 39, it being understood that similar relays will be provided for each phase for which protection is required, OM55 that the directional relays may be connected through phase-sequence networks as shown in Fig. 1.

Each of the three successive sectionalizing stations 25, 26 and 21 is provided with a single carrier-current transmitter, as indicated at 40, ll and 42, these transmitters being tuned respectively for 101,000 cycles, 103,000 cycles and 104,000 cycles.

Each of the sectionalizing stations 25, 26 mam associated filters 43", 44" and 45",

is as follows.

21 of Fig. 2 is provided, as in Fig. 1, with a coupling capacitor 3, a transmitter-coupling transformer 6, a receiver-coupling transformer I, 8, 9, a filter F passing the heat-frequency of 1000 cycles, a receiver-relay E, and a timing relay Z. At the switching station 25, however, the receiver relay E and the timing relay Z are associated with the directional element 34 which is responsive to fault-power flowing to the left, in line-section 2|. In the next switching station 26, the receiver relay E and the timing relay Z are associated with the directional element 3'1, which is responsive to fault-power flowing to the right, in line-section 23. In the next switching station 2?, the receiver relay E and the timing relay Z are associated with the directional element 38, which is responsive to fault-power flowing to the left, in line-section 23. These three receiver relays E serve to protect only one of the two line-sections connected to each switching station, and this protection is similar to that which has already been explained in connection with Fig. 1.

To protect the other line-section at each of the switching stations 25, 26 and 21, in Fig. 2, I have shown other receiver relays, as indicated respectively at 43, 44 and 45, which are utilized to- I directly trip the corresponding circuit-interrupters 29, 30 and 33, respectively, the receiver-relays being supplied with tripping contacts 43, 44 and 45', for this purpose. Since the receiver relays 43, 44 and 45 are utilized to actually open the associated circuit breakers when the receiver relays are energized, the connections must be such as to fulfill the conditions set forth in connection with Fig. 1, namely, that the fault-power direction must be into the protected line-section at each end thereof, as indicated by the condition of the carrier-current channel and by the condition of the directional relay at the switching station in question. 'The energizing coils of the receiver relays 43, 44 and 45 are thus connected to their and their tripping-contacts 43', 44' and 45' are connected, as in Fig. 1, in series with the contacts 3B .and 39' of the corresponding directional relays 35,

36 and 39, respectively.

It will be noted that the frequency-difference between the transmitters 411 and 41 of stations 25 and 26 is dilferent from that between the transmitters 4| and 42 of stations 26 and 21, thereby avoiding conflict, as indicated in the discussion of Fig. 1. The filters 43", 44" and are therefore tuned to pass 2,000 cycles, rather than 1,000

cycles, so as to respond selectively to carrier-current transmission at the remote end of only the respective sections (2!, 22 and 23) in which the receiver-relays 43, 44 and 45 are located.

The operation of the system shown in Fig. 2 The connection and disconnection of the several transmitters 40, 4! and 42 to the transmission-line sections 2|, 22, 23 and 24 is made responsive to the directional relays 34, 31 and 38, respectively, each transmitter being connected to the transmission line at all times except when its associated directional relay is moved to its actuated position, in which case, it

energizes a relay 34, 31 or 38, as the case may be, thereby opening the normally closed contact 5 of the latter, and interrupting the transmission of carrier current at that station, as in Fig. 1. In line-section 23 in Fig. 2, the protection is precisely the same as that which is shown in .Fig. 1, so far as the operation of the carriercurrent is concerned; that is, the normally maintained carrier-current is interrupted only in response to fault-current flowing into the protected line-section 23, so that the receiver relays E, at stations 26 and 21, are deenergized only when power of fault-magnitude is flowing into the far end of the protected line-section 23, thereby causing the receiver relays to drop and close their back contacts E1 and E2, precisely as has been described in connection with Fig. 1.

The line-section 22 in Fig. 2 is somewhat differently protected. In this case, the normally maintained carrier-current is interrupted only in the event of fault-current-fiow in the direction out of the protected line-section 22, so that the respective receiver filters 43" and 44 at sta tions 25 and 26 will fail to receive their beatfrequency of 2,000 cycles, only when power of faultmagnitude is flowing out of the far end of the protected line-section. In the event that a current of fault-magnitude flows into the sec-' tion 22 at either end, say, at station 25, the corresponding directional relay 35 will respond, closing its tripping contact 35.

If the fault-current flow is caused by an internal fault within the protected line-section 22, there will be an inwardly flowing fault-current at the other end 26 of the line-section 22, so that any fault-current flowing in the directional relay 3'! in the succeeding line-section 23,

at said end or station 26, will be in a direction ceiver relay 43 energized, and keeping its tripping-contact 43 closed. As soon, therefore, as the directional relay 35 closes its contact 35, a tripping-circuit will be completed through the contacts 35 and 43', to trip the circuit-breaker 29.

If, however, the power-in fault-current-fiow in the directional relay 35 had been caused by an external fault, not in the protected section 22, but in some section beyond it, then there would have been a similar fault-current-flow into the next adjacent line-section 23, instantly actuating the directional relay 37, and removing the 103,000-cycle carrier-current from the protected line-section 22 at station 26. This would instantly deenergize the receiver-filter 43 at the station 25, where the relaying operation is under consideration, deenergizing the receiver relay 43, and opening its tripping-contact 43', so that, by the time that the directional element completed its response to the power-in fault-current therein, and closed its contact 35', the receiver-filter 43" would have become deenergized, and the tripping-circuit would have been opened at the receiver-relay contact 43, so that the circuitbreaker 29 would not be opened.

In the line-sections 22 and 24 of Fig. 2, where the receiver relays 43, 44 and 45 must be energized in order to trip their associated breakers 29, 30 and 33, respectively, these receiver relays can be energized only when the carrier-current transmitters at the two ends of the protected.

make any special provision, such as the timing relaysZ' of Fig. 1,- to guard against the contingency of carrier-current failure in the linesections 22. and 2470f Fig. 2.

In the system shown in Fig. 2, it will readily be understood. that. the line-section 2| is protectedisimilarly, to the line-section 23, with a 1,000.c-ycle beat-frequency between the transrnltters at-.,lts; two ends, and with carrier removed lby,power-inflow of fault-current; while the-line-section 24 is protected similarly to the line-section 22, with a 2,000-cycle beat-frequency between the transmitters at its two ends, and with carrier. removed by power-out flow of fault-current.

Figs..3.- and. 4 show another modification in which theswitching operations may be carried outwith only'one high-frequency transmitter at each. switching station. This system utilizes a transmitter in each switching station, with a separate modulation-device for each line-section to be protected. at that station. The modulationsconsistof'superposed frequencies so chosen that, for each modulation-wave, there will be only. one. receiving relay tuned to that modula- 25;,-tion-frequency, in one of the lines under consideration, and this: receiving relay continuously determines the existence or non-existence of said modulation-wave and prevents the opening of its associated: circuit-breaker as long as the existence of: the. corresponding modulation-frequency; is indicatedby the relay. Even if numerous lines leave a station, it is possible to carry: outthissystem with only one high-frequency generator which produces the carrier wave at. each. station, the different high-frequency generators being preferably of different frequencies At each relaying station, tuned high-frequencyreceiving-circuits are provided, as by means of the coupling capacitors 3, or more elaborate tuning-devices, as previously explained,".and a time-relay is also provided, for instance as-shownin Fig. 1, which renders the section'protective device inoperative if a modulation wavefails-for acertain time, provided that the other requisites for the disconnectionoi. the section are not.fulfilled simultaneously during this period inthe relaying station under consideration.

In'-Fi'g. 3 is shown a single-line diagram of such an embodiment of my invention, in which it is assumed that the lines are paralleled at each relaying-station A, B and C. A two-circuit transmission system isindicated, .in which there are two parallel line-sections Hand 12 between stationsA andB, and two parallel line-sections I3 and M-betweenstations B and C. At each station, there is a high-frequency transmitter, which is indicatedmtt'li iniFig; 4, for station B, and the output /oi this transmitter is modulated in acgo cordance-with" a. particular frequency for each lineesectionconnected tothe station bus. The modulatormaredndicated in Fig.- 3 by triangles drawnsabove eachline-section at each station, thmtriangies;or. modulators .being denoted by the saslettervM'; withwaa subscript indicating the frequency, whichvaries from 400rcyclesto 750 cycles, im50+cycle-stepa Beloweach line-section, in Fig. 2;.thesreceiver relays atzthe several stations are indicatednbyicircles'designated by the letter E,

7o;with'-- subsoriptszindicative: of the frequency to which they are responsive.

Asshown in Fig. 4, the transmitter I5 located inastation B transmits .a high-frequency carriercurre'nt ofiisay;100,000'cycles, which is -modu-- a latediby means :of ,thealternating-current modulating generators M500, M550, M500, and M550. These modulating generators are connectedto a modulating circuit Iiiv of the transmitter 15, throughindividual filters l1, I8, 19 and 80, which are tuned to the respective modulation-frequencies, and also through normally closed relaycontacts 81, 82, 83 and 84, respectively, so that, in normal operation, all four modulation-frequencies are impressed upon the carrier-current wave. This modulated carrier-current is superimposed upon the transmission system by means of the transformer 6, which is connected in series with the grounded circuit including the coupling capacitor 3.

Fig. 4 also shows the receiver circuit provided at station B, the same being connected to the grounded coupling, circuit including the coupling capacitorr3, by means of a transformer 85. The received current is demodulated'by means of a rectifier 86, and by this means, demodulated current'is supplied to a receiver-circuit 81, to which the several receiver relays E400, E450, E700 and E150 are connected, through their respective filters 88, 89, Bland 9i.

In Fig. 4, the paralleling bus 92 at station B is connected to the ends of four line-sections H, 12, I3 and 14, each having its individual modulator and receiver, as indicated more clearly in Fig. 3. As the equipment for each line-section is the same, except for the tuning, a description and illustration of one will suifice for all, and hence I have shown, in Fig. 4, the equipment for only the line-section l4 atstation B. The directional element 31 for-this line-section is indicated schematically in accordance with the method of illustration adopted in Fig. 2, and it has normally closed back-contacts 84 which normally keep the 650-cycle modulator-generator M050 connected to the modulating circuit 16 of the carrier-current transmitter 15. -'Ihe directional element 31 has normally open front-contacts 93 which are closed only when current of fault magnitude flows from the bus 92 into the-protected line-section 14. These directional-relay contacts 93 are connected in the tripping circuit of the circuit breaker 94 whichis located in station B in the line-section 14. This tripping circuit also includes the backcontacts 95 of the receiver-relay E750, and the back-contacts'zi of the associated timing relay Z750 which is controlled by the receiver-relay as in Fig. 1.

The operation of the system shown in Figs. 3 and 4 is similar to that shown in Fig. 1, except that the modulation frequencies of demodulated receiver-waves are utilized, rather than beatfrequencies, for the purpose of determining the condition of the directional relay at the other end of the protected line-section. This modulated-carrier response may be either to the power-in flow or the power-out flow at the remote end of the protected line-section. In the particular embodiment shown in Figs. 3 and 4, the '750-cycle modulation which is characteristic of the remote end of the protected line-section 14 is maintained at said remote end at all times except when current of fault-magnitude is flowing in the -power-in direction at that end, and hence the receiver-relay E050, which responds to this modulation, is a lock-out relay which prevents the tripping of the circuit breaker 94 as long as this receiver-relay is energized, this function being accomplished by the opening of the backcontact 95 of the relay whenever the relay is energized. It is believed that the operation of the system shown in-Figs. 3 and. 4 will now be obvious in view of the explanations given in connection with Fig. 1.

I claim as my invention:

1. A carrier-current protective system for a transmission-line section, comprising two sources of carrier current of different frequencies coupled to the line-section, one at each end thereof, means for controlling the transmission and non-transmission of carrier at each end in some manner in 10 accordance with the occurrence or non-occurrence of predetermined line-circuit conditions at that end, and means at each end, selectively responsive to the beat-frequency of the two carrier-current sources, for obtaining an indication of the linecircuit conditions at the other end of the linesection.

2. A carrier-current protective system for a transmission-line including a line-section having circuit-interrupting means at each end thereof, said protective system including normally continuously operating sources of carrier current of different frequencies, normally continuously coupled to the line-section, one at each end thereof, means at each end of the line-section for selectively responding to the beat-frequency of the two carrier currents, means at each end of the line-section for temporarily interrupting the transmission of carrier from that end to the far end, but not interrupting the application of carrier from that end to the beat-frequency means at that same end, in response to predetermined abnormal line circuit conditions at said same end of the protected line-section, carrier-current circuit-interrupter controlling means at each end of the protected line-section for controlling the circuit-interrupting means at that end under the joint control of line-circuit conditions at that end and beat-frequency conditions at that end, and timing means responsive to a failure of beat frequency for a predetermined length of time for thereafter performing a predetermined function.

3. A carrier-current protective system for a transmission-line including a line-section having circuit-interrupting means at each end thereof, said protective system including normally continuously operating sources of carrier current of different frequencies, normally continuously coupled to the line-section, one at each end thereof, means at each end of the line-section for selectively responding to the beat-frequency of the two carrier currents, means at each end of the linesection for temporarily interrupting the transmission of carrier from that end to the far end, but not interrupting the application of carrier from that end to the beat-frequency means at the same end, in response to both the existence of fault-power conditions and the existence of a predetermined direction of power-flow in the protected line-section at said same end thereof, carrier-current circuit-interrupter controlling means at each end of the protected line-section for controlling the circuit-interrupting means at that end under the joint control of line-circuit conditions at that end and beat-frequency conditions at that end, and timing means responsive to a failure of beat frequency for a predetermined length of time for thereafter performing a predetermined function.

4. A carrier-current protective system for a transmission-line including a line-section having circuit-interrupting means at each end thereof, said protective system including normally continuously operating sources of carrier current of different frequencies, normally continuously coupled to the line-section, one at each end thereof, means at each end of the line-section for selectively responding to the beat-frequency of the two carrier currents, directional relay means at each end of the line-section for responding to the direction of power-flow at its own end of the line-section, but making said response only in the event of fault-power conditions in the transmission-line, means at each end of the line-section for temporarily interrupting the transmission of carrier from that end to the far end, but not interrupting the application of carrier from that end to the beat-frequency means at that same end, in response to an actuation of a directional relay means at said same end of the protected linesection, carrier-current circuit-interrupter con trolling means at each end of the protected linesection for controlling the circuit-interrupting means at that end under the joint control of an actuation of a directional relay means at that end and a condition of energization or nonenergization of the beat-frequency means at that end, and timing means responsive to a failure of beat-frequency for a predetermined length of time for thereafter performing a predetermined function.

5. A carrier-current protective system for a transmission-line including a line-section having circuit-interrupting means at each end thereof, said protective system including normally continuously operating sources of carrier current of different frequencies, normally continuously coupled to the line-section, one at each end there of, means at each end of the line-section for selectively responding to the beat-frequency of the two carrier currents, directional relay means at each end of the line-section for responding to the direction of power-flow into the protected line-section at its own end thereof, but making said response only in the event of fault-power conditions in the transmission-line, means at each end of the line-section for temporarily interrupting the transmission of carrier from that end to the far end, but not interrupting the application of carrier from that end to the beat-frequency means at that same end, in response to an actuation of said directional relay means at said same end of the protected line-section, carriercurrent circuit-interrupter controlling means at each end of the protected line-section for con trolling the circuit-interrupting means at that end under the joint control of an actuation of said directional relay means at that end and a non-energization of the beat-frequency means at that end, and timing means responsive to a failure of beat frequency for a predetermined length of time for thereafter performing a predetermined function.

6. A carrier-current protective system for a transmission-system including a plurality of serially connected line-sections, switching stations between said line-sections, and circuitinterrupter means for each line-section in each station, said protective system including a plurality of normally continually operating carriercurrent generators tuned to different frequencies, a single carrier-current generator being disposed in each switching station, means at each station for superimposing the carrier-current on the transmission system, line-current-responsive directional means at the several stations for temporarily interrupting the transmission of carrier being in accordance with power-flow to the right, and so on, in-response-toalternating directions of power-flow in succeeding stations, and carrier-channel receiver's-means individual to each line-section at each stationfor selectively responding to the controlled application of carrier at the other end of the particular line-section in question, for exercising a controllinginfiuence on the circuit-interrupter means' for said line-section.-

'7. A carrier-current protective systemfor a transmission-system including a plurality of serially connected line-sections, switching stations between saidline-sections, and circuit-interrupter means for eachline-section in each station, said protective system-including a plurality of carrier-current generators tuned to different frequencies,- a carrier-current generator being disposed in eachswitchingstation, means at each station for. superimposing,the-carrier-cur- I rent. on the: transmission-system, the beat-frequencies between any carrier-current generator and the carrier-current"generatorsat'other stations along the line being different, so as to pro- ,vide for selectivity, meansfor. controlling the transmission of carrier-at each end in accordance with line circuit conditions at that end, means, at each end of each line-section, selectively responsive to the beat-frequency of the two carrier-current sources-at the opposite-ends of that line-section, for obtaining'an indication of the line circuit conditions atthe otherend of the linesection, and means-forutilizing such indication in the control of the corresponding circuit-interrupter means.

8. A carrier-current protective system fora transmission-line including a line-section having circuit-interrupting means at each. end thereof, said protective I system including normally continuously operating sourcesof carrier. current of different frequencies, normallycontinuously coupled-to the line-section, oneateach endthereof, means at each end of the'line-seotion forselectivelyresponding to the beat-frequency of'the two carrier currents, power-out directional relay means at each end of the-line-section for responding to the direction of power-flow out of:the protected, line-section at its. own end thereof, but making said response only in the event of fault-power conditions in the transmission-line, power-in directional relay means ateach end of the line-section for responding to the direction of power-flow into'the protected line-section at its ownend thereof; but making'said response only in the event'of fault-power conditions in the transmission-line, means-at eachend of the line-section for temporarilylnterrupting the transmission of carrier from that end'tothe far end; but not interruptingthe application of carrier from that end to thebeat-frequency means at that same end, in response to an actuation of said power-out directional-relay-means at said same end of the protected line-section; carriercurrent circuit-interrupter controlling. means at each end of the protected line-sectiomfor: controlling the circuit-interruptingmeans atthat end under the joint control of an actuation-of said power-in directional-means at that end and a continued actuation of the beat-frequency means at that end, and timing meansresponsive to a failure of beat frequency for a predetermined length oftime for thereafter performing a predetermined function.

9. A carrier-current protective system for a transmission-system including a plurality of line-sections, .each having a terminal Y in a common bus at acertain-switching-statiomother switching station or stations at the other ends of said line-sections, and circuit-interrupter means for each line-section in each station, said protective system including a single carrier-current generator. in saidcertain switching-station, other carrier-current generator 'or generators -in saidiother station or stations, means for normally continuously coupling said carrier-current generatorsto-said transmission-system, said certain switching-station also including a plurality of modulation-means of different distinctive modulation-frequencies, one for each line-sectionterrninal associated with said common bus, means for separately controlling each modulation-means in accordance: with predetermined line-circuit conditions in its own line-section, and carrierchannel receiver-means at the other ends of each of .said line-sections for receiving the transmit-- controlling the-transmission of carrier at its ownend in accordance with line circuit conditions at that: end, and means at each end, selectively responsive to the condition with respect to carriercurrent transmission at the other end, unaffected by-the condition-with respect to carrier-current transmission at its own end, and jointly responsive also to a rotational-phase-sequence line-circuit condition at its own end, for protectingsaid line-section.-

11. Acarrier-current protective system fora polyphase transmission-line section, comprising two normally transmitting sources of carrier current coupled to the'line-section, one at each end-thereof, means for controlling the transmission-ofcarrier at each end, phase-sequence-responsive means at each end of the line-section, for controlling said carrier-controlling means in response to a predetermined rotational-phasmsequence-line-circuit condition'at' its own end, and means at each end, jointly responsive to the condition with respect to carrier-current transmission at the other end and to arotational-phasesequence line-circuit condition at its own end, for. protecting said line-section.

12. A carrier-current protective system-for a polyphase transmission-line section, comprising two normally transmitting sources of carrier current coupled-to the line-section, one at each'end thereof, means for interrupting the transmission of carrier at each end, phase-sequence powerdirectionally responsive means at each end of the quence power-directional line-circuit condition at" itsowns end, for protecting saidline-section.

Ill

:- of signal current coupled to said communicating channel, one at each end thereof, a phase-sequence relay at each end of the line-section for interrupting the transmission of effective signal current at its own end in response to a predeter- 10 3 mined rotational-phase-sequence line-circuit condition at its own end, and means at each end, jointly responsive to the condition with respect to signal-current transmission at the other end and to a rotational-phase-sequence line-circuit s condtion at its own end, for protecting said linesection.

14. A protective system for a polyphase transmission-line section, comprising means for providing a communicating channel between the two ends thereof, two normally transmitting sources of signal current coupled to said communicating channel, one at each end thereof, means for interrupting the transmission of signal current at each end, a phase-sequence relay at each end of ggi'the line-section for controlling said signal-current-interrupting means in response to a predetermined rotational-phase-sequence power-directional line-circuit condition at its own end, and means at each end, jointly responsive to the condition with respect to signal-current transmission at the other end and to a rotational-phasesequence power-directional line-circuit condition at its own end, for protecting said line-section.

15. A carrier-current protective system for a.

a5ip olyphase transmission-line section, comprising two sources of carrier current coupled to the linesection, one at each end thereof, negative-phasesequence-responsive means at each end for controlling the transmission of carrier at its own end min accordance with line circuit conditions at that end, and means at each end, selectively responsive to the condition with respect to carrier-current transmission at the other end, unaffected by the condition with respect to carrier-current transmission at its own end, and jointly responsive also to a negative-phase-sequence line-circuit condition at its own end, for protecting said line-section.

16. A carrier-current protective system for a polyphase transmission-line section, comprising two normally transmitting sources of carrier current coupled to the line-section, one at each end thereof, means for controlling the transmission of carrier at each end, phase-sequence-responsive means at each end of the line-section, for controlling said carrier-controlling means in response to a predtermined negative-phase-sequence line-circuit condition at its own end, and means at each end, jointly responsive to the condition with respect to carrier-current transmission at the other end and to a phase-sequence line-circuit condition at its own end, for protecting said line-section.

17. A carrier-current protective system for a ...polyphase transmission-line section, comprising two normally transmitting sources of carrier current coupled to the line-section, one at each end thereof, means forinterruptingthe transmission of carrier at each end, phase-sequence power-directionally responsive means at each end of the linesection, for controlling said carrier-interrupting means in response to a negative-phase-sequence line-circuit condition at its own end, which indicates the presence of a fault on the protected- 1ine-section side of the phase-sequence powerdirectionally responsive means, and means at each end, selectively responsive to a failure of carrier-current transmission at the other end, unaffected by the condition with respect to carriercurrent transmission at its own end, and jointly responsive also to a negative-phase-sequence power directional line-circuit condition at its own end, for protecting said line-section.

18. A protective system for a polyphase transmission-line section, comprising means for pro- Vidlng a communicating channel between the two ends thereof, two normally transmitting sources of signal current coupled to said communicating channel, one at each end thereof, a phase-sequence relay at each end of the line-section for interrupting the transmission of effective signal current at its own end in response to a predetermined negative-phase-sequence line-circuit condition at its own end, and means at each end, jointly responsive to the condition with respect to signal-current transmission at the other end and to a negative-phase-sequence line-circuit condition at its own end, for protecting said linesection.

19. A protective system for a polyphase transmission-line section, comprising means for providing a communicating channel between the two ends thereof, two normally transmitting sources of signal current coupled to said communicating channel, one at each end thereof, means for interrupting the transmission of signal current at each end, a phase-sequence relay at each end of the line-section for controlling said signal-current-interruptingmeans in response to a predetermined negative-phase-sequence power-directional line-circuit condition at its own end, and means at each end, jointly responsive to the condition with respect to signal-current transmission at the other end and to a negative-phase-sequence power-directional line-circuit condition at its own end, for protecting said line-section.

20. A carrier-current protective system for a transmission-line including a line-section having circuit-interrupting means at each end thereof, said protective system including normally continuously operating sources of carrier current of different frequencies, normally continuously coupled to the line-section, one at each end thereof, means at each end of the line-section for selectively responding to the beat-frequency of the two carrier currents, means at each end of the line-section for temporarily interrupting the transmission of carrier from that end to the far end, but not interrupting the application of carrier from that end to the beat-frequency means at that same end, in response to predetermined line circuit conditions at said same end of the protected line-section, carrier-current circuitinterrupter controlling means at each end of the protected line-section for controlling the circuitinterrupting means at that end under the joint control of line-circuit conditions at that end and beat-frequency conditions at that end, and timing means responsive to a failure of beat frequency for a predetermined length of time for thereafter performing a predetermined function.

21. A carrier-current protective system for a transmission-line including a line-section having circuit-interrupting means at each end thereof, said protective system including normally continuously operating sources of carrier current of different frequencies, normally continuously cou pled to the line-section, one at each end thereof, means at each end of the line-section for selectively responding to the beat-frequency of the two carrier currents, means at each end of the line-section for temporarily interrupting the transmission of carrier from that end to the far end, but not interrupting the application of carrier from that end to the beat-frequency means at that same end, in response to the existence of a predetermined direction of power-flow in the protected line-section at said same end thereof, carrier-current circuit-interrupter controlling means at each end of the protected line-section for controlling the circuit-interrupting means at that end under the joint control of line-circuit conditions at that end and beat-frequency conditions at that end, and timing means responsive to a failure of beat frequency for a predetermined length of time for thereafter performing a predetermined function.

22. A carrier-current protective system for a transmission-line including a line-section having circuit-interrupting means at each end thereof, said protective system including normally continuously operating sources of carrier current of different frequencies, normally continuously coupled to the line-section, one at each end thereof, means at each end of the line-section for selectively responding to the beat-frequency of the two carrier currents, directional relay means at each end of the line-section for responding to the direction of power-flow at its own end of the line-section, means at each end of the line-section for temporarily interrupting the transmission of carrier from that end to the far end, but not interrupting the application of carrier from that end to the beat-frequency means at that same end, in response to an actuation of a directional relay means at said same end of the protected line-section, carrier-current circuit-interrupter controlling means at each end of the protected line-section for controlling the circuit-interrupting means at that end under the joint control of an actuation of a directional relay means at that end and a condition of energization or non-energization of the beat-frequency means at that end, and timing means responsive to a failure of beat frequency for a predetermined length of time for thereafter performing a predetermined function.

23. A carrier-current protective system for a transmission-line including a line-section having circuit-interrupting means at each end thereof, said protective system including normally continuously operating sources of carrier current of different frequencies, normally continuously coupled to the line-section, one at each end thereof, means at each end of the line-section for selectively responding to the beat-frequency of the two carrier currents, directional relay means at each end of the line-section for responding to the direction of power-flow into the protected linesection at its own end thereof, means at each end of the line-section for temporarily interrupting the transmission of carrier from that end to the far end, but not interrupting the application of carrier from that end to the beat-frequency means at that same end, in response to an actuation of said directional relay means at said same end of the protected line-section, carrier-current circuit-interrupter controlling means at each end of the protected line-section for controlling the circuit-interrupting means at that end under the joint control of an actuation of said directional relay means at that end and a non-energization of the beat-frequency means at that end, and timing means responsive to a failure of beat frequency for a predetermined length of time for thereafter performing a predetermined function.

24. A carrier-current protective system for a transmission-system including a plurality of serially connected line-sections, switching stations between said line-sections, and circuit-interrupter means for each line-section in each station, said protective system including a plurality of normally continually operating carrier-current generators tuned to different frequencies, a single carrier-current generator being disposed in each switching station, means at each station for superimposing the carrier-current on the transmission system, line-current-responsive directional means at the several stations for temporarily interrupting the transmission of carrier at the points where there exists a predetermined direction of flow of power, the response in one station being in accordance with power-flow to the left, the response in the next station being in accordance with power-flow to the right, and so on, in response to alternating directions of power-flow in succeeding stations, and carrier-channel receiver-means individual to each line-section at each station for selectively responding to the controlled application of carrier at the other end of the particular line-section in question, for exercising a controlling influence on the circuit-interrupter means for said line-section.

25. A carrier-current protective system for a transmission-line including a line-section having circuit-interrupting means at each end thereof, said protective system including normally continuously operating sources of carrier current of different frequencies, normally continuously coupled to the line-section, one at each end thereof, means at each end of the line-section for selectively responding to the beat-frequency of the two carrier currents, power-out directional relay means at each end of the line-section for responding to the direction of power-flow out of the protected line-section at its own end thereof, power-in directional relay means at each end of the line-section for responding to the direction of power-flow into the protected line-section at its own end thereof, means at each end of the line-section for temporarily interrupting the transmission of carrier from that end to the far end, but not interrupting the application of carrier from that end to the beat-frequency means at that same end, in response to an actuation of said power-out directional relay means at said same end of the protected line-section, carriercurrent circuit-interrupter controlling means at each end of the protected line-section for controlling the circuit-interrupting means at that end under the joint control of an actuation of said power-in directional means at that end and a continued actuation of the beat-frequency means at that end, and timing means responsive to a failure of beat frequency for a predetermined length of time for thereafter perform,- ing a predetermined function.

26. A protective system for a polyphase transmission-line section having a line-conductor for each phase, said system comprising means for providing a communicating channel between the two ends of the protected line-section, two normally transmitting sources of signal current coupled to said communicating channel, one at each end thereof, a relay at each end of the line-section, responsive only to an unbalance condition in the protected line-section, means at each end for interrupting the transmission of effective signal current at its own end in response to an actuation of said unbalance relay at that end, and

means, at each end, jointly responsive to the condition with respect to signal-current transmission at the other end and to a negative-phasesequence line-circuit condition at its own end, for protecting said line-section.

27. In a polyphase transmission-line section having a line-conductor for each phase, and a circuit-interrupting means at each end thereof, a protective system for substantially simultaneously opening the circuit-interrupting means at both ends only in the event of such a fault-condition in the protected section as is accompanied by an unbalance between the currents in said line-conductors, said protective system comprising means for providing a communicating chan nel between the two ends of the protected linesection, two normally transmitting sources of signal current coupled to said communicating channel, one at each end thereof, a relay at each end of the line-section, responsive only to an unbalance condition in the protected line-section, means at each end for interrupting the transmission of effective signal current at its own end in response to an actuation of said unbalance relay at that end, and means at each end, jointly responsive to the condition with respect to signalcurrent transmission at the other end and to a negative phase-sequence line-circuit condition at its own end, for controlling the circuit-interrupting means at its own end.

HERMAN N NEUGEBAUER. 

